Ha! No, it's a new build (less than 3 years old), and they haven't been 'cleaned', as such.

Two earlier points - we suspect that when we got him he was maybe only 4 or 5 weeks old, rather than 6 as the owner said. So maybe he did leave his mum too early.
Also, he is on his own quite a lot each day - but I try not to leave him for too long at a time. At least until he's neutered.
He's been doing it again this morning. And he bit me when I was stroking him. Grrr!